For new testers the common pitfalls that I have seen are:
– Start to test without a good understanding of the requirements.
– Not to cover a complete range of scenarios from a user perspective.
– Difficulty to share steps to reproduce issues with developers.
– Duplicate efforts on certain issues that has not been implemented yet.
– Don’t have automated tests in place for features that were already tested.
I did some of them myself when I was starting as a tester!